Permaculture, as its name implies, can also be  thought of as permanent culture or permanent agriculture. So in contrast to most modern agricultural systems and even most modern towns and cities where resources are used in  a more linear system (used once then throw "away"), permaculture at its foundation designs agricultural systems and human settlement patterns to be able to part of a closed loop, cyclical system. Ecosystems are closed loop, wherein resources are never lost and only take on a different form, so in designing human system this way as well, as laram mentioned, permaculture attempts to mimic nature and in so doing uses the available resources more effectively.

Whether we like to believe it or not, even humans are bound by the laws of nature, and if we choose to live outside of those bounds, ultimately we will not survive--even though it is a truth that, amongst other things, is not very fun to consider.  There is a certain amount of resiliency and delayed feedback built into natural systems and so the long term impact of the scale and degree to which humans are altering the planet, is not always immediately visible. (Though even when it is visible its also a matter of being able to identify the symptoms). So, it is a very good idea to begin to live on this earth as if we actually want to be sustained by it, to live within the bounds of the ecosystem that we call home. Practicing permaculture is one such attempt.

It is claimed to be a good idea because it trains individuals in a core set of principles who can then build more sustainable settements. Permaculture allows for lower costs, an increase in community values, and overall efficiency. It has also been criticized for its potential to spread environmental weeds, reflecting a divide between native plant advocates and permaculture.

Permaculture is where agriculture systems and human settlements are designed like natural ecosystems. They are such a great idea because they promote efficiency and sustainability. In natural environments every part of the ecosystem plays its role and supports all the other parts.